Currently, the number of radio and television stations that broadcast their signals wirelessly or by cable has become very large and the schedules of each broadcaster are extremely disparate.
Both in an indoor domestic or working environment and outdoors, we are constantly subject to hearing, intentionally or unintentionally, audio that arrives from radio and television sources.
Listening and viewing of a radio or television program can be classified in two different categories: of the active type, if there is a conscious and deliberate attention to the program, for example when watching a movie or listening carefully to a television or radio newscast; of the passive type, when the sound waves that reach our ears are part of the audio background, to which we do not necessarily pay particular attention but which at the same time does not escape from our unconscious assimilation.
Indeed in view of the enormous number of radio and television stations available, it has become increasingly difficult to estimate which networks and programs are the most followed, either actively or passively.
As is known, this information is of fundamental importance not only for statistical purposes but most of all for commercial purposes.
In this context, so-called sound matching techniques, i.e., techniques for recording audio signals and subsequently comparing them with the various possible audio sources in order to identify the source to which the user has actually been exposed at a certain time of day, have been developed.
Sound recognition systems use portable devices, known as meters, which collect the ambient sounds to which they are exposed and extract special information from them. This information, known technically as “sound prints”, is then transferred to a data collection center. Transfer can occur either by sending the memory media that contain the recordings or over a wired or wireless connection to the computer of the data collection center, typically a server which is capable of storing large amounts of data and is provided with suitable processing software.
The data collection center also records continuously all the radio or television stations to be monitored, making them available on its computer.
In order to define which radio or television stations have been heard during the day, each sound print detected by a meter at a certain instant in time is compared with said recordings of each of the selected radio and television stations, only as regards a small time interval around the instant being considered, in order to identify the station, if any, to which the meter was exposed at that time.
Typically, in order to minimize the possibility of achieving false positives and false negatives, this assessment is performed on a set of consecutive sound prints.
Although the basic technology is sufficiently developed and affirmed, it has been found that current sound recognition devices are not sufficiently reliable. False recognitions are in fact often obtained or the recognition of a certain audio source fails, especially in the presence of ambient noise which partially covers the sound emitted by a radio or television, as often occurs in real life.